How To ... Move Objects to a Surface的疑问之处

文章名：How To ... Move Objects to a Surface


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 macroscript MoveToSurface category:"HowTo"

(

fn g_filter o = superclassof o == Geometryclass

fn find_intersection z_node node_to_z =

(

local testRay = ray node_to_z.pos [0,0,-1]

local nodeMaxZ = z_node.max.z

testRay.pos.z = nodeMaxZ + 0.0001 * abs nodeMaxZ

intersectRay z_node testRay

)

on isEnabled return selection.count > 0

on Execute do

(

target_mesh = pickObject message:"Pick Target Surface:" filter:g_filter

if isValidNode target_mesh then

(

undo "MoveToSurface" on

(

for i in selection do

(

int_point = find_intersection target_mesh i

if int_point != undefined then i.pos = int_point.pos

)--end i loop

)--end undo

)--end if

)--end execute

)--end script

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看了一个小时，没看懂，划红线的是不明白的地方，ray 什么意思一直搞不明白，google翻译成射线，很别扭，不知道专业的怎么称呼

还有undo 的用法，帮助文档也没看明白

文档中有一句话是这么解释undo在本段代码中的作用： In case a valid object has been picked, enable an undo context ，没读懂，也请指点一下